1. Field of the Invention
The present invention relates to a power supplying method for an injection molding machine which has a plurality of kinds of servo amplifiers with different allowable voltages and a transformer for transforming a plurality of kinds of voltages.
2. Description of the Related Art
An injection molding machine is provided with independent servo motors for each driving part (i.e., servo motors for injection, for metering (screw rotation), for mold opening/closing, and for an ejector). Required output of each of these servo motors differs depending on a driving part to which the servo motor is applied. Especially, a motor with higher output power than other servo motors is employed as a servo motor for injection which injects resin into a mold.
If voltage or current of a servo amplifier which drives the servo motor is increased, output of the servo motor is increased accordingly. However, such an increase of current would encounter a limit of output due to a maximum current of a power element in the servo amplifier. Accordingly, for increasing an output further, not only a current to be supplied to the servo amplifier but also a voltage to be applied to the servo amplifier are required to be increased. In such a case, a servo amplifier with input voltage of 400 V is applied as a servo amplifier adaptable to a high voltage, in place of a general servo amplifier with input voltage of 200 V.
As described above, a high output power can be obtained with such a 400 V servo amplifier. On the other hand, in case where such a servo amplifier is used, withstand voltage performance of electric components in the servo amplifier has to be improved. Moreover, in order to improve such withstand voltage performance, it is necessary to extend distances between conductors such as cables and wires, which inevitably makes the servo amplifier larger in size. As a result, if a 400 V servo amplifier is employed for each of servomotors (i.e., servo motors for injection, for metering, for mold opening/closing, and for an ejector) equipped in each driving part in an injection molding machine, these servo amplifiers would undesirably occupy large portions of storage space for control parts of the injection molding machine. Consequently, such an injection molding machine could not store all of these servo amplifiers.
For storing all servo amplifiers in an injection molding machine, it is preferable to apply a 400 V servo amplifier only in a driving part requiring a 400 V servo amplifier, while using a 200 V servo amplifier in a servo motor not requiring such a high output, such as a servo motor for mold opening/closing and a servo motor for an ejector, since a 200 V servo amplifier is smaller in size than a 400 V servo amplifier with the same output power.
FIG. 2 shows an injection molding machine including a 200 V servo amplifier and a 400 V servo amplifier.
An injection molding machine 1 is provided inside with a servomotor at each driving part (a servo motor for injection 22, a servomotor for screw rotation 24, a servomotor for mold opening/closing 26, and a servo motor for an ejector 28). Furthermore, each of the servo motor has a servo amplifier individually (a servo amplifier for injection 12, a servo amplifier for screw rotation 14, a servo amplifier for mold opening/closing 16, and a servo amplifier for an ejector 18). In addition, the injection molding machine 1 includes inside a transformer 30 to transform a voltage of 200 V (voltage of facility power supply) into a voltage of 400 V. The transformer 30 boosts a voltage of 200 V input as a main power supply 2 to a voltage of 400 V for a 400 V servo amplifier.
An injection molding machine disclosed in Japanese Patent Application Laid-Open No. 2007-168177 is the same as the injection molding machine shown in FIG. 2 in that they include both a 200 V servo amplifier and a 400 V servo amplifier in a mixed manner. However, in the case of Japanese Patent Application Laid-Open No. 2007-168177, input voltage value is 400 V and therefore a transformer is provided for a 200 V servo amplifier.
A production facility like an injection molding machine may be relocated between factories for reasons of manufacturing in a factory. Voltage of facility power supply in a factory differs among factories or regions. Therefore, if an injection molding machine is adaptable to only any one voltage of 200 V and 400 V, it is necessary to additionally install a transformer between a facility power supply in a factory and the injection molding machine so as to supply power to the injection molding machine by boosting or lowering a voltage depending on a voltage of the facility power supply. If a proper voltage is not supplied to the injection molding machine, the injection molding machine does not operate properly.
FIG. 3 shows an example of an injection molding machine in which a transformer 35 is additionally installed outside the injection molding machine.
In FIG. 3, a transformer 35 for transforming a voltage from 400 V to 200 V is additionally installed outside an injection molding machine 1, as a voltage of a facility power supply is 400 V while a voltage of a main power supply of an injection molding machine 1 is 200 V. Thus, by installing the transformer 35 outside the injection molding machine 1, it becomes possible to supply a voltage that corresponds to a voltage required for a main power supply of an injection molding machine, even when a voltage of facility power supply in a factory changes, thereby enabling the injection molding machine to operate. However, an additional installation of a transformer is accompanied by problems of cost and installation location. Especially, as the size of an injection molding machine becomes larger, capacity of a transformer increases accordingly, which may also increase a burden for a user.